Hepatic electrical stimulation

ABSTRACT

A method of providing electrical stimulation to a liver of a subject includes providing one or more stimulatory electrodes to the liver of the subject and providing electrical stimulation to the liver of the subject. The method further relates to methods of reducing risk factors of metabolic syndrome, treating diabetes, treating a subject having eating disorders and reducing glucose levels of a subject.

FIELD OF THE INVENTION

The present invention relates generally to hepatic electricalstimulation and, more particularly to hepatic electrical stimulation forthe treatment of risk factors of metabolic syndrome.

BACKGROUND OF THE INVENTION

Throughout this application various publications are referenced. Thedisclosures of each of these publications in their entireties are herebyincorporated by reference in this application.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C illustrates the relationship of blood glucose levels at 0,15, 30, 45, 60, 75 and 90 minutes after electrical stimulation undervarious parameters. FIG. 1A shows results for 14 Hz stimulation and shamstimulation; FIG. 1B shows results for 40 Hz stimulation and shamstimulation; and FIG. 1C shows results for 100 Hz stimulation and shamstimulation.

FIGS. 2A-2C illustrate a method of placing a device on the surface of aliver, in accordance with some embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the “vagal nerve” or the “vagus nerve” refers to thetenth of twelve paired cranial nerves. The vagal nerve starts in thebrainstem and extends to the abdomen. A branch of the vagal nerve thatextends to the liver is referred to herein as the “hepatic vagal nerve”or the “hepatic vagus nerve”.

As used herein, electrical stimulation of the liver as used hereinrefers to stimulation of any portion of the liver of the subject,including intrahepatic stimulation and stimulation to the outer surfaceof the liver. In one embodiment, electrical stimulation is provided tothe hepatic portal vein. In one embodiment, stimulation is provided tothe bile ducts, which include the right and left hepatic ducts, thecommon hepatic duct and the cystic duct. In one embodiment, electricalstimulation is provided to the afferent hepatic vagal nerve. In analternative embodiment, electrical stimulation is provided to theefferent hepatic vagal nerve. In one embodiment, electrical stimulationis provided to both the afferent and efferent vagal nerves. In oneembodiment, electrical stimulation of the liver refers to stimulation ofthe visceral fat, such as the omentum, of the subject.

As used herein, the “afferent vagal nerve” refers to the vagal nervethat carries impulses toward the central nervous system. “Efferentnerves” refers to nerves which carry impulses away from the centralnervous system.

In one embodiment, one stimulatory electrode is provided. In analternative embodiment, more than one stimulatory electrode is provided.In one embodiment, unipolar stimulation is provided. In unipolarstimulation, one stimulatory electrode is placed on or in the liverwhile a second stimulatory electrode is placed in or on the subjectother than in or on the liver.

“Risk factors of metabolic syndrome” as referred to herein mean riskfactors as described in Table 1 of Rosenson et al., Curr. Opin. Cardiol.19:480-87(2004). Risk factors include fasting plasma glucose of aboveabout 110 mg/dL, insulin resistance, abdominal obesity or obesitydefined as a body mass index of above about 30 kg/m², waist girth aboveabout 40 inches in men and about 35 inches in women, serum triglyceridesof about 150 mg/dL, serum HDL cholesterol of below about 40 mg/dL in menand 50 mg/dL in women and/or blood pressure of above about 130/85 mmHg.

As used herein, “metabolic syndrome” is defined to mean a system bywhich a subject is identified to be at high risk for coronary heartdisease and/or type 2 diabetes. A subject is said to fulfill thecriteria for metabolic syndrome if they have at least three of theabove-identified risk factors.

“Reducing” one or more risk factors of the metabolic syndrome refers toreducing or eliminating the risk factors of the subject. This includesreducing levels of fasting plasma glucose of the subject to below about110 mg/dL, in one embodiment by reducing fasting plasma glucose of thesubject to below about 100 mg/dL, decreasing insulin resistance of thesubject, decreasing abdominal obesity (such as decreasing waist girth tobelow about 40 inches in men and below about 35 inches in women),decreasing obesity or decreasing the body mass index of the subject tobelow about 30 kg/m², decreasing serum triglycerides of the subject tobelow about 150 mg/dL, increasing serum HDL cholesterol to above about40 mg/dL in men and 50 mg/dL in women and/or decreasing blood pressureto below about 130/85 mmHg.

A subject refers to an animal, including a human, subject. For non-humananimal subjects, the particular structure of the hepatic vagal nerve maydiffer from that of a human. For such non-human animal subjects, thehepatic vagal nerve, as used herein, refers to that non-human animal'sknown hepatic vagal nerve and liver.

In one embodiment, the first step of the present invention includesselecting a subject which would benefit from the method of the subject,such as, for example, selecting a subject who has one or more riskfactors of the metabolic syndrome. In one embodiment, a step of thepresent invention includes determining an initial reading of one or moreof the risk factors of metabolic syndrome, such as, for example, levelsof fasting plasma glucose of the subject, insulin resistance of thesubject, abdominal obesity (such as waist girth of the subject), bodymass index of the subject, serum triglycerides of the subject, serum HDLcholesterol and/or blood pressure. The initial reading is determinedprior to providing hepatic electrical stimulation to the subject. In oneembodiment, a step of the present invention includes determining areading of the one or more of the risk factors of metabolic syndromeafter hepatic electrical stimulation is provided to the subject.

An “electrode” or a “stimulatory electrode” refers to a conductor ofelectricity through which current enters a medium (a subject), whereas a“sensor” refers to a conductor of electricity through which currentleaves a medium (a subject). Typically, for hepatic uses, thestimulatory electrodes and sensors are constructed of teflon-insulatedwires such as are used for cardiac pacing wires. The stimulatoryelectrode is electrically connected (i.e., conductively connected) to asource of electrical current (often referred to as a pacemaker or astimulator, where a set pattern of electrical current is delivered), andthe sensor is electrically connected to a device for determining thelevel of electrical current “sensed” by the sensor (an electricalrecorder, for example). In one embodiment, the stimulatory electrodesand the source of electrical current are contained in a microstimulator,i.e. both are included in one unit which is placed directly on in theliver of the subject.

The stimulatory electrode is thus used to “generate” electrical currentand the sensor is thus used to “detect” electrical current. In oneembodiment, electrical stimulation is provided to a subject without theuse of sensors. In an alternative embodiment, sensors are used in amethod of the present invention to determine the level of electricalstimulation provided to the subject. In one embodiment, sensors are usedto determine the level of one or more risk factors of metabolicsyndrome.

In an embodiment where sensors are used in a method of the presentinvention, “operatively connected” is used herein to refer to theconnection between the stimulatory electrode and the sensor, andindicates that the operation of one is connected to the operation of theother. In particular, the sensor connects to a device which determinesthe level of electrical stimulation and/or the level of one or more riskfactors of the metabolic syndrome detected by the sensor. Arepresentation of that level is then fed to the source of electricalcurrent that is electrically connected to the stimulatory electrode. Thesource of electrical current is provided with a programmable computercircuit that enables the level from the sensor to determine, or dictate,the operation of the source (i.e., electrical current is generated bythe source and fed through the stimulatory electrode in response to andan in relation to the amount of the level of the risk factor sensed bythe sensor). In one embodiment, levels determined by the sensor includelevels of plasma glucose, levels of serum triglycerides, levels of serumHDL cholesterol and/or blood pressure readings.

“Positioning” a stimulatory electrode or a sensor refers to placement ofthe stimulatory electrode or sensor on or in a subject.

“Periodically” refers to evenly or unevenly spaced time intervals.

“Differs from” refers to a statistically significant variation betweentwo compared values, and therefore does not always require a differencein orders of magnitude. It should be apparent that where small valuesare compared, statistically significant variations can likewise be verysmall, and where large values are compared, statistically significantvariations can be large. Conversely, “substantially equals” refers to astatistically insignificant variation between two compared values.

“Electrical field stimulation” refers to the generation of an“electrical field”, which indicates that the area of distribution of theelectrical current from the stimulation encompasses the entire areabetween and/or surrounding two or more stimulatory electrodes, and“field” is used to imply that the two or more stimulatory electrodes arepositioned at least about three centimeters apart (thus the term “field”to differ from prior stimulations where the two electrodes of a pair arepositioned in close proximity to one another and do not generate a“field”).

A “device” refers to any suitable item which can readily be and isdesirable to be placed in or around the liver of the subject. Suchdevices can include, for example, stimulatory electrodes and sensors foruse in the method of the subject invention.

In one embodiment, “providing electrical stimulation” relates toproviding long pulse stimulation, providing short pulse stimulation orproviding a combination of long pulse and short pulse stimulation. “Longpulse” electrical stimulation refers to an electrical signal which has along width, such as in an order of from about 1 to about 900milliseconds, or about 2 to about 600 milliseconds, has a pulseamplitude of from about 0.1 mA to about 20 mA and has a frequency offrom about 0.02 Hz to about 10 Hz. “Short pulse” electrical stimulationrefers to an electrical signal which has a short width, such as in anorder of from about 50 to about 999 microseconds, or about 100 to about300 microseconds, pulse amplitude of from about 0.1 to about 20 mA andhaving a frequency which from about 5 Hz to about 500 Hz. Any number oflong pulses, short pulses and/or combination of long pulses and shortpulses is provided to the subject over the course of the electricalstimulation.

In one embodiment, providing electrical stimulation refers to anelectrical signal which includes a train of pulses. A train of pulsesrefers to a method in which the stimulus is composed of repetitivetrains of short pulses and is derived from the combination of twosignals a) continuous short pulses with a high frequency and b) acontrol signal to turn the pulses on and off, such as x seconds on and yseconds off. The addition of x and y then determines the frequency ofthe pulse train. The train will be set on for a period of from about0.01 seconds to about 10 seconds followed by a period where the pulsesare off from a period of from about 0.01 to about 10 seconds. The pulseswithin the train have a frequency of from about 1 to about 30 Hz, in oneembodiment from about 10 to about 20 Hz, in one embodiment from about 12to about 16 Hz, and in one embodiment about 14 Hz. The pulses have awidth of about 0.1 to about 2 ms, in one embodiment from about 0.2 toabout 1 ms, and in one embodiment about 0.3 ms. The pulses have anamplitude of from about 0.1 mA to about 20 mA, in one embodiment formabout 0.5 to about 8 mA, in one embodiment about 1 to about 5 mA, in oneembodiment about 2 to about 5 mA and in one embodiment about 4 mA. Adiscussion of trains of short pulse electrical stimulation is containedin Zhang, et al., Current Treatment Options in Gastroenterology,9:351-360 (2006).

In one embodiment, electrical stimulation is provided to the subject fora time period of from about one minute up to about 180 minutes.

With these definitions in mind, the present invention provides a methodof electrical stimulation of a subject which includes providing one ormore electrodes to the liver of the subject and providing electricalstimulation to the liver of the subject.

Another embodiment of the invention relates to a method of reducing oneor more risk factors of the metabolic syndrome of a subject whichincludes providing one or more electrodes to the liver of the subjectand providing electrical stimulation to the liver of the subject underconditions effective to reduce the one or more risk factors of metabolicsyndrome of the subject.

Another embodiment of the invention relates to a method of treating asubject having diabetes by carrying out a method of the presentinvention. Controlling glucose levels of a subject is an important partin treating diabetes of the subject.

Another embodiment of the invention relates to a method of treating asubject having coronary heart disease by carrying out the method of thepresent invention. Controlling glucose levels is an important part intreating coronary heart disease of the subject (Smith, S C., Am. J. Med.120(3 Supp. 1):S3-S11(2007).

Another embodiment of the invention relates to positioning one or moresensors relative to the subject to detect levels of the one or more riskfactors of the metabolic syndrome, such as plasma glucose levels, serumtriglycerides, serum HDL cholesterol and/or blood pressure and providingone or more stimulatory electrodes relative to the subject where the oneor more stimulatory electrodes are operatively connected to the one ormore sensors to provide electrical stimulation to the subject based onthe levels of the one or more risk factors detected by the sensors.

Another embodiment of the invention relates to a method of treating asubject suffering from an eating disorder. Eating disorders include, forexample, obesity.

Another embodiment of the invention relates to a method of placing adevice on the surface of the liver or into the liver (for example, underthe surface of the liver) of a subject from the exterior of the subject.The method includes inserting an end of a needle having an interior borefrom the exterior of the subject proximate to the surface of or into theliver of the subject. The device is inserted through the interior boreof the needle until the device engages at least the surface of theliver. In one embodiment, the device is inserted into the liver of thesubject. The needle is removed, leaving the device in or on the liver.Wires connected to the device will pass through the skin of the subjectto the exterior of the subject. The source of electrical current, suchas the stimulator, is connected to the wires. In one embodiment, themethod of placement of the device includes viewing the liver of thesubject with an ultrasound.

Referring now to FIG. 2, a specific embodiment of a method of placing adevice on the surface of the liver is shown. As shown in FIG. 2A, needle14 is used to place device 16 on the surface of liver parenchyma 12 ofsubject 10. Needle 14 consists of end 20 and interior bore 18. Interiorbore 18 houses device 16. In some embodiments, device 16 is an electrodethat is connected to wires.

As shown in FIGS. 2B and 2C, the method consists of inserting end 20 ofneedle 14 from the exterior of subject 10 to the surface of liverparenchyma 12 of the subject. Device 16 is then inserted throughinterior bore 18 of needle 14 until the device engages at least thesurface of liver parenchyma 12. Next, needle 14 is removed, leavingdevice 16 on liver parenchyma 12. In some embodiments, wires connectedto device 16 pass through the skin of subject 10 to the exterior of thesubject.

Although not meaning to be bound by theory, previously, humoral factorswere the main focus of investigation of metabolic syndrome. Neurocentricmodels, such as those of Schwartz et al., Science 307:375-79 (2005),discussed that defects in the negative feedback regulation of energybalance and glucose production predispose a subject to weight gain andinsulin resistance. More recently, however, the role of nerves in themetabolic syndrome have been investigated. Studies have shown that thehepatic vagal afferents are an important means of communication betweenthe liver and the rest of the body, including adipose tissue (Berthoud,H R, The Anatomical Record, Part A, 280a:827-835(2004)). The autonomicnervous system (ANS), including both the vagus nerve and the sympatheticnerves, also plays a role in mediating the central nervoussystem/hypothalamic control of the metabolism (Berthoud, H R,Neuroscience & Biobehavioral Reviews 26:393-428 (2002)). According toone theory, imbalance in the ANS is an important cause of the metabolicsyndrome (Kreier et al., Diabetes 52:2652-56(2003). One proposedmechanism by which the one or more risk factors of metabolic syndromeare reduced by hepatic electrical stimulation in a method of the presentinvention is via stimulation of the afferent vagal fibers. The afferentvagal fibers are thought to originate mainly around the portal vein andits branches and respond to changes in portal glucose and fatty acidconcentrations, exciting nuclei in the brain that, in turn, controlfeeding behavior and regulation of energy metabolism via both hormonaland neural (vagal efferent and sympathetic) output to critical organsincluding adipose tissue (Berthoud, H R, The Anatomical Record, Part A,280a:827-835(2004)). In turn, activation of these fibers has been shownto improve systematic insulin sensitivity and lower blood glucose levelsalong with reductions in adipose tissue (Schwarz, G J, Cell Metabol.4(2):103-05(2006)). These effects can be reversed by both hepaticsensory vagal ablation and sympathetic blockade (Uno et al., Science312:1656-1659 (2006)).

An alternative mechanism by which the one or more risk factors ofmetabolic syndrome are reduced by hepatic electrical stimulation in amethod of the present invention is via stimulation of the hepatic vagalefferents. According to Lautt, W W, J. Pharmacol. Sci. 95:9-17(2004),the liver produces an unidentified factor termed hepatic insulinsensitizing substance (HISS). HISS is produced in response topost-prandial insulin and stimulates skeletal muscle to take up glucose.According to this research, vagal efferent tone is required forproduction of HISS.

EXAMPLE 1

Although the liver has been known to have a nerve supply for a longtime, relatively little is known about its physiological role. There isrecent experimental evidence that neuronal reflexes consisting of theafferent vagus from the liver and efferent sympathetic nerves to adiposetissues, may regulate energy expenditure, systemic insulin sensitivity,glucose metabolism, and fat distribution between the liver and theperiphery (Uno et al., Science 312: 1656 (2006)). These authors showedthat expression of peroxisome proliferator-activated receptor (PPAR)-g2in mouse liver markedly decreased peripheral adiposity. These changeswere accompanied by increased energy expenditure and improved systemicinsulin sensitivity. Hepatic vagotomy and selective afferent blockage ofthe hepatic vagus revealed that the effects on peripheral tissuesinvolve the afferent vagal nerve. By providing electrical stimulation tothe liver parenchyma it was hypothesized that the ascending limb of thisreflex could be stimulated and achieve the same effects.

Methods

Animal Preparations

Eight male SD rats weighing 300-350 grams were used. They were kept at24° C. with a 12:12 hour light-dark cycle. The animals were fed withlaboratory food and water.

Surgery and Placement of Hepatic Electrodes

After an overnight fast, rats were given general anesthesia (2%isoflurane inhalation in oxygen 2 L/min), prepared for abdominal surgeryand an abdominal midline incision was performed. For the hepaticelectrical stimulation, one pair of cardiac pacemaker wires wereimplanted into two hepatic leafs respectively. Three electrodes werefixed on anterior chest wall subcutaneously for recording the EKG. Thefree end of wires were then tunneled through the anterior abdominal wallsubcutaneously and exited from the back neck skin. Midline incision wassutured and rats were left to recover in their separate cages. Food andwater were abundantly provided. They were left 7 days to recover.

Hepatic Electrical Stimulation and Plasma Glucose Assessment

The HES parameters evaluated in this study were as follows:

-   -   1. 40 Hz, pulse width of 0.3 ms, on time of 2 sec, and off time        of 3 sec and 4 mA    -   2. 100 Hz, with the other parameter the same as above    -   3. 14 Hz, width of 0.3 ms, 0.1 s on and 5 s off, 4 mA.    -   4. Sham stimulation.

Four different parameters were evaluated on 4 separate day for each ratwith a interval of 3 days.

All experiments were conducted between 9 and 11 am. After an overnightfast, rats were randomized receiving HES for 60 minutes after beingadministered a dose of 20% glucose in a volume of 5 ml/kg. Blood glucoselevel was monitored at 0, 15, 30, 45, 60, 70, and 90 minutes afterglucose loading by tail nipping. It was assessed with a commerciallyavailable glucometer (RELI ON® Ultima, Solartek Products Inc., Alameda,Calif.). A drop of blood was applied to the tip of the test strip andthe readings of plasma glucose were displayed automatically.

Results:

The three different stimulation parameters yielded different results asfollows:

14 Hz stimulation (these parameters are currently being used for gastricelectrical stimulation for the treatment of gastroparesis using theMedtronics device, Enterra (Lin et al., Digestive Diseases & Sci. 48(5):837-48 (2003) resulted in highly significant (P<0.0001 by 2-way ANOVA)effects on blood glucose (See FIG. 1A).

40 Hz stimulation (using parameters currently being employed for thetreatment of obesity by Transneuronix (Chen, J D Z. Obesity Surgery14(Supp. 1): 28-32 (2004)) revealed the opposite effect (also highlysignificant, P<0.0001) (See FIG. 1B).

100 Hz stimulation did not produce any effect on blood glucose (See FIG.1C).

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions and the like can bemade without departing from the spirit of the invention and these aretherefore considered to be within the scope of the invention as definedin the claims which follow.

1. A method of electrical stimulation of an afferent vagal nerve of asubject having a liver parenchyma, said method comprising: positioningone or more stimulatory electrodes in or on the liver parenchyma of thesubject; and providing electrical stimulation to the liver parenchyma ofthe subject; wherein electrical stimulation to the liver parenchymastimulates the afferent vagal nerve.
 2. The method of claim 1, whereinthe electrical stimulation is provided for a period of up to about 180minutes.
 3. The method of claim 2, wherein the electrical stimulation isprovided at a frequency ranging from about 5 Hz to about 500 Hz.
 4. Themethod of claim 3, wherein the electrical stimulation is provided as aseries of pulses, wherein each pulse is provided for about 0.1 ms toabout 2 ms.
 5. A method of reducing one or more risk factors ofmetabolic syndrome in a subject, wherein said subject has a liver andone or more risk factors of metabolic syndrome, said method comprising:carrying out the method of claim 1 under conditions effective to reduceone or more risk factors of metabolic syndrome.
 6. The method of claim5, wherein the one or more risk factors of metabolic syndrome areglucose levels more than about 110 mg/dL, obesity, insulin resistance,levels of serum triglycerides more than about 150 mg/dL, serum HDLcholesterol levels less than about 50 mg/dL, or blood pressure levelsmore than about 130/85 mmHg.
 7. The method of claim 5, wherein theelectrical stimulation is provided for a period of up to about 180minutes.
 8. The method of claim 7, wherein the electrical stimulation isprovided at a frequency ranging from about 5 Hz to about 500 Hz.
 9. Themethod of claim 8, wherein the electrical stimulation is provided as aseries of pulses, wherein each pulse is from about 0.1 ms to about 2 ms.10. The method of claim 5, wherein the one or more risk factors is aglucose level more than about 110 mg/dL.
 11. The method of claim 10,wherein the glucose level is reduced to less than about 100 mg/dL.
 12. Amethod of treating diabetes in a subject, said method comprising:carrying out the method of claim 1 under conditions effective to reducea glucose level of the subject, wherein the glucose level of the subjectis more than about 110 mg/dL.
 13. A method of treating coronary heartdisease in a subject, said method comprising: carrying out the method ofclaim 1 under conditions effective to reduce a glucose level of thesubject, wherein the glucose level of the subject is more than about 110mg/dL.
 14. A method of treating a subject with an eating disorder, saidmethod comprising: carrying out the method of claim 1 under conditionseffective to increase weight loss in the subject.
 15. A method ofplacing a vagal nerve stimulatory device on a surface of the liverparenchyma or into the liver parenchyma of a subject, wherein theplacement occurs from the exterior of the subject, said methodcomprising: inserting an end of a needle with an interior bore from theexterior of the subject to the surface of or into the liver parenchymaof the subject; inserting the device through the interior bore of theneedle until the device engages at least the surface of the liverparenchyma; removing the needle, wherein the device is placed on thesurface of or into the liver parenchyma of the subject; wherein thedevice is an electrode.